Hydrocephalus is a condition that is also sometimes known as “water on the brain”. People with this condition have abnormal accumulation of cerebrospinal fluid (CSF) in the spine and ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head, convulsion, and mental disability. The elevated intracranial pressure may cause compression of the brain, leading to brain damage and other complications.
Hydrocephalus is usually caused by a blockage of CSF outflow in the ventricles or in the subarachnoid space over the brain. The condition is called internal hydrocephalus and it results in increased CSF pressure. The production of CSF continues, even when the passages that normally allow it to exit the brain are blocked. Consequently, fluid builds inside the brain causing pressure that compresses the nervous tissue and dilates the ventricles. Compression of the nervous tissue usually results in irreversible brain damage. If the skull bones are not completely ossified when the hydrocephalus occurs, the pressure may also severely enlarge the head. In a normal healthy person, CSF continuously circulates through the brain and its ventricles and the spinal cord and is continuously drained away into the circulatory system. In a hydrocephalic situation, the fluid accumulates in the ventricles, and the skull may become enlarged because of the great volume of fluid pressing against the brain and skull. Alternatively, the condition may result from an overproduction of the CSF fluid, from a congenital malformation blocking normal drainage of the fluid, or from complications of head injuries or infections.
Internal hydrocephalus can be successfully treated by placing a drainage tube (shunt) between the brain ventricles and the abdominal cavity to eliminate the high internal pressures.
It involves the placement of a ventricular catheter into the cerebral ventricles to bypass the flow obstruction and drain the excess fluid into other body cavities, from where it can be reabsorbed. Most shunts drain the fluid into the peritoneal cavity (ventriculo-peritoneal shunt, or VP shunt), but alternative sites include the right atrium (ventriculo-atrial shunt), pleural cavity (ventriculo-pleural shunt), and gallbladder. A shunt system can also be placed in the lumbar space of the spine and have the CSF redirected to the peritoneal cavity (LP Shunt).
Shunt systems are usually also designed to function using the pressure differential between the brain and another part of the body and to regulate the drainage flow using a programmable valve. With the VP shunt, a surgical procedure provides an opening in the skull through which an entry catheter is introduced and passed through the brain tissue into the ventricles. The catheter is attached to a pump or valve, which is positioned subcutaneously against the exterior of the skull, to control fluid flow. A second exit catheter, usually also subcutaneous in position, is also attached to the pump and leads to the peritoneal cavity.
One example of such a shunt is described in US2004082900 concerning a cerebral spinal fluid (CSF) shunt comprising a ventricular cavity for receiving CSF in a drainage chamber for passing the CSF to a patient's abdominal cavity. An anti-syphon valve controls CSF flow from the ventricular cavity to the drainage chamber. The valve utilizes a thin, flexible portion of the ventricular cavity which operates an underlying pressure control membrane. The membrane overlies a valve opening that permits CSF flow from the ventricular cavity into the drainage chamber. In place of the membrane, a spring-biased ball can be used to open and close the valve opening.
Another example is US2004068201 describing devices and methods for removing cerebrospinal fluid (CSF) from a CSF space of a patient at relatively constant flow rates for patients having normal intracranial pressures, e.g. patients not suffering from hydrocephalus. The devices and methods provide drainage paths which permit the removal of CSF at relatively low flow rates, usually below 0.2 ml/day, at normal intracranial pressures, e.g. an intracranial pressure between −170 mm of H2O in upright patients and 200 mm of H2O in reclining patients. The system operates by externally receiving an output signal from a flow sensor in a flow lumen of the implanted CSF drainage shunt, said signal being representative of CSF flow through the flow lumen, wherein the flow sensor is selected from the group consisting of a thermal device, a dye release device, a differential pressure measuring device, a turbine meter, an angular momentum measuring device, a positive displacement measuring device, and an accumulator.
The document DE19541377A1 describes a valve unit that is located within a drainage channel to the head of the patient and contains two pressure controlled valves. The high pressure valve opens at a (programmable) pressure of say 40 cm of water, whilst the low pressure valve opens at a fixed pressure of 13 cm of water. In series with the low pressure valve and parallel to the high pressure valve is a position switch which, when the patient is standing (presenting an angle between 0 deg. and 45 deg.), closes the channel which is parallel to the high pressure valve. With the patient lying down, (angles between 45 deg. and 90 deg.) the drainage channel opens. The position switch comprises a pendulum and a valve seat which is closed by the pendulum. The pendulum is a ball (6) with an eccentric weight (8) which is located within a hollow area (10) within a housing (9). The pendulum can swing in every direction. The valve is connected to a circular channel (7) in the housing and the ball has channels (11) located in it as well. When the patient is upright the pendulum moves to ensure that the channels in the ball are sealed and thus the valve is closed. When the patient lies down, the channels in the ball connect to the circular channel whose outlet (13) leads to the drainage channel. The high pressure valve is bridged and the low pressure valve can operate.
None of these documents, however, describes that a number of factors would influence the intracranial pressure, such as the position and the activity of the person.